The present invention relates generally to the field of analog and digital signal processing counting randomly occurring pulses and more particularly to the field of high speed analog and digital signal processing for neutron coincidence counting. This invention is the result of a contract with the Department of Energy (Contract No. W-7405-ENG-36).
A high speed analog detector with digital output is essential in the field of neutron time-correlation measurement for nuclear materials and for other applications wherein a plurality of rapidly and randomly occurring pulses are to be detected and counted with assured accuracy. Neutron correlation, or coincidence, counting is commonly used in both active and passive nondestructive assay (NDA) instrumentation as a unique signature of the fission process. Thermal-neutron counting systems utilizing polyethylene moderators and .sup.3 He or BF.sub.3 gas-filled proportional counters have been limited in counting rate capability by the charge-collection time and the applification circuitry. This has resulted, in many cases, in large counting losses for materials with high nuclear material content and, in some cases, unreliable assays because of excessive counting rates.
Prior art neutron time-correlation, or coincidence, counting circuits used extensively during the past decade for nuclear material measurements and safeguards are detailed by J. S. Swansen, P. R. Collinsworth, and M. S. Krick in "Shift-Register Coincidence Electronics System for Neutron Counters," Los Alamos National Laboratory Report LA-8319-MS, April 1980. The prior art systems described are limited in counting speed and accuracy due in part to coincidence dead times in the order of 2.4 microseconds. An improvement to counting rates of over 150 kilo-pulses per second/channel and 1 million pulses per second total for six channels with a deadtime of only about 0.7 microseconds as achieved by the present invention represents a significant advancement in the state of the art.
It is therefore an object of the present invention to provide a high-performance neutron time-correlation counter having improved counting rate, accuracy and stability.
It is another object of the present invention to provide a plurality of improved detectors that can function in conjunction with each other, each having separate visual output of pulse detection and each being either enabled or disabled without affecting the operation of the others.